Transmission and reception of intelligence



y 2, 1935- s. G. FRANTZ El AL 2,006,989

I TRANSMISSION AND RECEPTION OF INTELLIGENCE Filed Nov. 19, 1930 5 Sheets-Sheet 1 INVENTORS 5-6 FRANTZ BY 5. 5. 31 c CHEN ATTORNEY July 2, 1935.

s. G. FRANTZ ET AL 2,006,989

TRANSMISSION AND RECEPTION OF INTELLIGENCE s Shets-Sheet 2 Filed Nov. 19, 1930 4. E lIlll/l/Ek llllllllll ill INVENTORS 5.6. FRANTZ B. 5. M CUTCHEN Patented July 2, 1935 UNITED \STATES PATENT OFFICE 'rItANsMIssIoN AND RECEPTION F INTELLIGENCE Samuel G. Frantz and Bronson S. McCutchen,

Princeton, N. J., assignors to Radio Corporation of America, a corporation of Delaware Application November 19, 1930, Serial No. 496,595

24 Claims. (Cl. 2506) This invention relates generally to the transthe use of our system will be the lessening of the mission and reception of intelligence and is speefiect of atmospheric disturbances upon the recifica-lly directed towards improving the quality ce ver. of the received intelligence. The measure of the effect of atmosp h di More specifically, the present invention relates turb nce r o h r in rf on the quality 5 to systems and methods for maintaining the relaof reception is the ratio of interference intensity tions between the various increments of the into signal intensity, d this effect W therefore telligence issuing from an electrical energy transbe most Pronounced when the Signal intensity s lating device at a receiving point substantially low th the p t y during w 10 proportional to the relations between the various 1811181 Signals. the transmitted Signal intensity 10 corresponding increments of the original intelliw l lw be greater n i w ld b w re there gence, no compression of intensity range before trans- An object of the invention i t provide novel mission, and therefore the efiect of interference and eiiicient method of transmission and recepis minimized. In other w d w e wea si na s 5 tion of signals. are being transmitted the energy will be more Another object of the present invention is the amplified before it is d r du ali Ofl With achieving of clear fidelity of reproduction at the a result th t rdinary atmosp disturbances receiving end of radio signals and in particular will o obscure he i a music, by partial or total compression of the in- This invention relates to and comprises the go tensity range, or range of mod l ti t t above described compression and expansion of transmittin e and corresponding expansion f intensity range, and means for accomplishing the the intensit range at the receiving end. compression a d e pansion- In the proposed system t degree or percent- In the subject matter hereinafter described age of modulation applied to the carrier wave at there are Proposed for this purpose three Ways of the transmitting end insteadofbeing madedirectinforming the receiving apparatus as to what 25 ly proportional to the intensity of the signal in the amount of expansion is necessary- The three microphone circuit is made to sufier a smaller cases m be clajssified asfonowsi percentage variation than the latter. This may radio channelbe called range compression or sub-proportional Vanatlon f Ga ner frequency.

modulation. Thus, in this system a weak signal e use of the resldual, vanatlon of modu" 30 will be more amplified before it is used for modu- Iation percentage itself as the signal which lation t will a Strong Signal A feature of our municates to the receiving apparatus how much invention is then that the intensity range or the the should be amp1ifiedratio between maximum and minimum percent- T slmpl.est case 9 the latter would age of modulation of the transmitted radio siganthmlc suP-pmpmmnal range compresslon at 35 l is 195 th t intensity range of the original the transmitter with corresponding logarithmic signal. The extent or degree of this compression -pr p r ional range expansion at the reof intensity range may in practice result in about ceiver- Expressed mathematlcauy we the same ratio of maximum to minimum percent- I k I 1 40 a e of modulation as is at present obtained by 49 manual control at broadcasting stations; or, the 1 1 compression may be carried much further even h e to the limit at which there is a total obliteration I =Origina1 intensity Y f in y range and the Signal is transmitted I2=Transmitted intensity of modulation at constant percentage modula In general, Ia=Receiver output intensity 45 in the present system the intensity range will be It; and It; are constants compressed but not obliterated. and a=a constant 1 A th e e g end of the present System In using the system described in the third submeans are pr d to rte-expand the intensity division it is obvious, of course, that the intensity 50 range 110 that existing in the Original alrange must not be completely obliterated. 50 These means at the receiver must be so arranged An object of the present invention is to provide as to work in correspo d with e oompresa specially constructed bridge arrangement for sion effected at the transmission station. effecting the desired compression at the trans- At this point we desire to emphasize the fact mitter and expansion at the receiver.

that one of the benefits that will be derived from Another object of the invention is the provision 55 of a plurality of said specially constructed resistance bridges arranged in cascade.

Another object ,of the present invention is to provide means for performing the desired compression and expansion by varying the carrier frequency.

Still another object of the present invention is to provide a separate channel for the transmission from transmitter to receiver of the information necessary for the receiver to adjust itself for proper amplification.

Still other objects of the invention will be apparent from the following description of typical circuits according to our invention illustrated in the accompanying drawings, in which Figure 1 illustrates a transmitter arrangement of one form of our invention utilizing a so-called temperature bridge;

Figure 2 illustrates diagrammatically a method by which two or more temperature bridges may be cascaded;

Figure 3 illustrates diagrammatically a receiver in accordance with our invention employing a temperature bridge arrangement for receiving and appropriately expanding signals transmitted from a system such as shown in Figure 1;

Figure 4 illustrates diagrammatically an alternative method of range compression in a transmitter circuit;

Figure 5 illustrates a receiver adapted to be used in conjunction with a transmission system such as shown in Figure 4;

Figure 6 illustrates diagrammatically a range compression transmission circuit utilizing the variable frequency carrier method;

Figure 7 illustrates diagrammatically a receiver for receiving signals and appropriately amplifying them for a transmission system such as that shown in Figure 6;

Figure 8 illustrates diagrammatically a transmitter adapted to perform the desired compression of the signal intensity and utilizing a separate channel for the transmission of the information to the receiver; and,

Figure 9 is an appropriate receiver tem disclosed by Figure 8.

Referring to Figure 1 a microphone circuit is shown composed of microphone 5, transformer I and the usual source of current 6. An amplifier for the current generated in the microphone circuit is shown generally at 8 coupled to the microphone circuit by means of the transformer I. The output of the amplifier 8 is connected to a temperature bridge 9 by means of conductors I3 and I2 connected to diagonal points I4 and I5 respectively of the bridge 9. The other ,two diagonal points of the bridge 9, namely, I 6 and I! are connected by conductors H and I respectively, to a modulator and radio frequency energy source circuit of any well known design. Referring more particularly to the temperature bridge I, 2, 3 and 4 compose the four elements thereof. Elements I and 4 are of the same material and elements 2 and 3 are of some other material having a different temperature co-efiicient of resistance than said first material. The wires it will be evident are appreciably heated by the passage of the currents due to the signal voltage applied from the amplifier output. With maximum signal voltage the bridge is hottest and the resistances are so proportioned that under this condition the bridge is almost balanced; that is, the ratio of bridge output voltage to bridge input voltage is a minimum. With very for the syslow input voltage the bridge is comparatively cold and has a maximum of unbalance and hence the ratio of output to input voltage is a maximum. Thus the bridge acts as a non-proportional attenuator, attenuating strong signals more than weak ones. While we do not intend to limit ourselves to any particular construction of the bridge one way on which the bridge could be constructed would be of small wires about the size of flashlight bulb filaments. Either I and 4 or 2 and 3 may be resistances so designed as to heat but little. Broadly, the term temperature bridge as used herein includes any network with input and output connections in which the ratio of output to input voltage varies according to the input voltage as a result of change of resistance of any of the elements of the network due to heating by the current passing through it.

Attention is now directed to Figure 2. In said figure conductors I2 and I3 correspond to the -conductors I2 and I3 leading from the output of the amplifier 8 of Figure 1.- Conductors I2 and I3 are connected to diagonally opposite points 2| and 20 respectively of the temperature bridge I8. The other two diagonally opposite points 22 and 23 of the bridge I8 are connected by conductors 24 and 25 respectively to two diagonally opposite points 21 and 26 respectively of a second temperature bridge device I9. The other two points of said last named bridge, namely, 28 and 29 may be connected either to another similar bridge arrangement or to the modulator and radio frequency energy source as shown by Figure 1 through the medium of conductors I0 and II. It will thus be evident that in the arrangement shown any number of temperature bridges may be connected in cascade for obtaining any results desired.

Attention is now directed to Figure 3 which shows a receiver adapted to properly expand the signals which were compressed by the transmitter shown in Figure 1. In Figure 3, 30 represents generally a stage of audio frequency amplification in an ordinary radio receiver. Coupled to the output of said stage by means of transformer 3| is a temperature bridge 32 in accordance with our invention. It will be noted that the secondary of the transformer 3| is connected by conductors 33 and 34 to two diagonally opposite points of said bridge 32. The other two diagonally opposite points of the bridge are connected by means of conductors 35 and 36 to the input of an amplifier generally shown at 31. The output of this amplifier 31 is connected by means of conductors 39 and 38 to a receiving instrument shown generally as a telephone receiver 40. The bridge 32 is made up of elements I, 2, 3 and 4 which operate in a somewhat similar manner to that described above in connection with Figure 1 except that in the case of the receiver, the bridge will be" in approximate balance for minimum signal, so that in Figure 3 the greater the applied electromotive force e across the secondary of the transformer 3I the greater will be the resistance of elements I and 4 compared to the resistance of elements 2 and 3. This condition causes an increased unbalance of the bridge and an increased output current. It is to be distinctly understood that while we have shown only one bridge arrangement in the receiver shown in Figure 3 two or more such bridge arrangements may be arranged in cascade as shown in Figure 2.

Attention is now directed to Figure 4 which shows an alternative method of range compression and Figure which shows a receiver for receiving signals sent out from an arrangement lator tube 42 is also adapted to receive an alternating electro-motive force at some supersonic frequency from an oscillator. For this purpose we have shown the supersonic oscillator diagrammatically as 43 feeding the alternating electromotive force to the input of the modulator tube through the transformer 44 the secondary of which is placed in the grid cathode circuit of the modulator tube 42. It will be seen that with the arrangement so far described the output of the modulating tube 42 is then in the form of a supersonic carrier wave modulated by the voice frequency. An auxiliary winding on the microphone transformer 41 is connected to the grid of a biased rectifier tube 45 which tube as will be seen from the drawings has its input circuit coupled to the microphone circuit. A biasing means 46 is shown connected in the grid-cathode circuit of tube 45. It will be seen that with the connection as shown, that is, because of the bias the direct component of the plate current of this rectifier tube 45 varies with changes in intensity of the voice signal or rather of the microphone circuit energy. This variation in plate current is used to change the bias on the grid of an amplifier tube 41 which tube has its input circuit coupled to the output of tube 42. The arrangement of the circuit including the tube 41 is such that the variation in the plate current of tube 45 changes the bias on the grid of tube 41 in such a way that an increase of voice signal input causes a decrease in the gain in the ampli fier tube 41 by biasing its grid more" negatively. For this purpose there is provided in the plate circuit of tube 45 a resistance 48 in series with the plate current supply 50. The input circuit of the tube 41 includes a condenser 49 and means comprising a conductor 52 and a conductor con- .nected to a variable contact for placing any desired portion of the resistance 48 across the condenser 49. The output of the amplifier tube 41 is fed to a detector 54 through a coupling transformer 53. The detector tube serves the purpose of separating the audio component of the energy pansion system at the receiver is essentially the inverse of that of the range compressor at the transmitter. Referring to Figure 5 there is shown a usual antenna circuit 51 coupled to a radio frequency amplifier tube 59 through the medium of a tuned circuit 58. The output of the tube 59 is coupled to the input of a second radio frequency amplifier 6| through a transformer 64. This second radio frequency tube has connected in its grid cathode circuit a condenser II shunted by a source of current 13 and a resistance 1!. The connection between the source of current 13 and the resistance 1| is made variable for a purpose which will be later described. The output of tube 6| is connected to the input'of a detector tube 63 through a coupling transformer 62 and the output of the detector tube is coupled to any desired type of audio frequency amplifier shown generally as 65 through an audio transformer 64. An auxiliary detector tube 61 is provided which is shown also coupled to the antenna through the medium of tuned circuit '66. This tuned circuit is tuned synchronously with the main tuning of the receiver in any desired manner now in use, such as any of the well known uni-control systems. The audio output of tube 51 is fed into a biased rectifier tube 69 through the medium of transformer 68. Due to the biasing on the tube 69 the plate current thereof increases with an increase in signal intensity. It should be noted that part of the plate circuit of tube 69 is made up of the resistance 1| in series with source of current 14. A condenser 15 is shown connected across the anode and cathode of tube 69. The increase of plate current in tube 58 causes an increased voltage drop in the resistance 19 which as described before is in the plate circuit of tube 69 as well as in the grid circuit of tube 6i and this drop is used to decrease the bias on the radio frequency amplifier tube 8! as is evident from the drawings, thus increasing the gain in this stage and increasing the output intensity. It should here be noted that in the range compressor shown in Figure 4 there is shown a large capacity. 11 connected across the plate and filament of the tube 45 and a choke coil 18 in series with the plate resistance 48. The object of this capacity and inductance is to prevent rapid variations in the bias of the amplifier tube 61 so rapid as to constitute an audio frequency disturbance. In Figure 5, condenser 15 has a similar function.

Attention is now directed to Figure 6 in which we have shown an arrangement in which for purposes oi communicating to the receiver the amount that the receiver should amplify there is employed a system which makes use of so-called carrier wave frequency variation. In said figure the usual microphone circuit comprising microphone 5 and source 5 is shown coupled by means oftransformer 60 to the input of a range compressor shown generally as 6i. This range compressor may be of any suitable design, such as, any one of the range compressors shown in this application. The output of the range compressor 5! is coupled to a modulator by means of a coupling transformer 62. The modulator may be of any desired form and is shown generally at 63. The voice input transformer 60 has a third winding 64 which is connected to a grid ofa biased rectifying tube 65. This tube is arranged so that variations in the intensity of the voice current are manifested as a change in the magnitude of the direct component of the plate current of this biased rectifier tube. In the plate circuit of tube 85 there is the winding of a solenoid 65. The

armature 61 of said solenoid is arranged to oper ate on a plate 68 of a small condenser 69 which is connected in parallel with the main tuning condenser of the main carrier frequency master oscillator 1|. This masteroscillator feeds into the modulator circuit 53 through a coupling 12 and the modulated carrier wave is relayed into the radio frequency power amplifier shown generally at 14 through the coupling transformer 12. From the power amplifier 14 the modulated carrier wave properly amplified is radiated as is usual through an antenna 15. It is evident from what has preceded that the frequency of the carrier wave generated at H is varied or wobbled in accordance with the intensity of the voice input at 5 by means of the arrangement comprising the solenoid 66, armature 61 and variable condenser 69. The receiver for the system shown in Figure 6 will now be described.

Reference will now be had to Figure I in which I5 represents a receiving antenna. Coupled to the antenna I5 through coupling transformer I5 is the usual radio frequency amplifier shown generally at 11. The amplifier output is directed to a variable gain tube 10 through a transformer I9. The output of the variable gain tube I8 goes to a detector tube 80 and from thence to an audio amplifier in customary manner. Coupled to the antenna is a pickup coil 8| which forms part of the input circuit of a space discharge device 02. The grid circuit of this tube is so arranged that it receives an electromotive force from a local oscillator shown generally at 83 through a transformer 84. This oscillator must be tuned with the main receiver and may be tuned simultaneously therewith or separately if desired. The oscillator is not tuned to the exact carrier frequency but it is a frequency different from the nominal carrier frequency by some standard amount, say, 1000 cycles. At the transmitting end the arrangement is such (see Figure 6) that with no voice input the radiated frequency is the nominal carrier frequency, therefore, at the receiving end (see Figure 7 with no voice input there will be a beat frequency in the output of tube 82 of 1000 cycles. Tube 82 is biased so as to give this beat product. The output of tube 82 is coupled to a tuned circuit 84' which is permanently tuned to respond to a frequency of 1000 cycles. The tuned circuit it will be noted forms a portion of the input circuit of tube 85 which tube is biased so as to rectify. A variation in the original signal intensity at the transmitting end, say an increase of signal intensity, will produce an increasing variation of carrier frequency from normal carrier frequency. The beat note in the output of tube 82 will thus change from 1000 cycles to some less amount. This results in a decrease in the response of tuned circuit 84' and a decrease therefore in the input of tube 85. Tube 85 is biased by means of source 88 so that a decrease in the grid input results in a decrease in the direct component of the plate current. This decreases the voltage drop across a resistance 81 in the plate circuit of tube 85 which resistance is connected in the grid return of the radio frequency amplifier tube I8 in the main receiver. Thus, an increase in original signal intensity decreases the plate current of tube 85, thus, decreasing the negative bias of the radio frequency amplifier tube I8 and increasing the gain of the main signal in this tube. In this way the amplification is greatest for greatest original signal intensity.

In the plate circuit of tube 85 there is shown a choke coil 90 and a large condenser19, the condenser being connected across the plate and filament of the tube 85. The purpose of this arrangement is to prevent the 1000 cycle note or others from being applied to the grid of the tube I8.

In any of the methods thus far described there may be a. slight delay in the operation of the apparatus in circuits intended to control the intensity atthe transmitting and receiving ends, that is, in the compressors and expanders. If this delay is found large enough to produce objectionable results its effect may be counteracted in the systems using separate channel or frequency variation by interposing in the circuit at the transmitting station an electric delay circuit of any well known kind, of time constant long enough to compensate for the objectionable delay. This electric delay circuit must be placed in the main voice circuit after the branch take-off has been made for operating the frequency variation or the separate channel signal.

Reference is now made to Figure 8 in which we have shown our invention embodying the use of a separate channel for the transmission from the transmitter to the receiver of the information necessary for the receiver to adjust itself to an appropriate degree of amplification. In Figure 8 a microphone circuit including microphone 5, source of current 6 and transformer I is shown connected through the transformer I00 to a range compressor IOI which may be of any suitable design such as any of those shown herein. The output of the range compressor is shown as leading to a radio or wire channel No. I. The microphone transformer I00 also has a third winding I02 connected to the input of a biased rectifier tube I03 which is so connected that its plate current varies with changes in the signal intensity. A large capacity I04 is shunted across the plate and filament of tube I03 and a choke coil I05 is placed in series with the plate of tube I 03 in order to prevent rapid changes in the direct component of the plate current. This direct component passes through a resistance I06 which is shown associated with the plate circuit of the tube I03. The voltage drop across this resistance is used to change the bias of an amplifier tube I0'I. The amplifier tube has impressed upon its grid a low frequency electromotive force from a suitable oscillator I08. This frequency may be of the order of l00 to 1000 cycles. The output of the amplifier tube I01 is put on to the radio or wire channel which is to be used for purposes of range expansion control. In the drawings this is referred to as channel No. 2.

Attention is now directed to Figure 9 which shows a receiver which can be used for receiving signals in accordance with the system disclosed in Figure 8. In Figure 9 the main signal comes in on radio or wire channel No. I, is pased through an amplifier H0 and is impressed upon the grid of tube II I. The output of this tube is connected to a usual detector I I2 from there to the customary amplifier I I3 and to the telephone circuit I II. The intensity signal comes in over radio or wire channel No. 2, is directed through an amplifier I I5 and is then impressed upon the grid of tube I I6 which is a biased rectifying tube so arranged that the direct component of its plate current is a function of the intensity of the signal impressed upon its grid. A condenser 'I I1 and choke coil II8 are provided and shown as connected to the plate circuit of tube II6 for the same purpose as previously described in connection with Figure 8, reference being had to condenser I04 and coil I05. Variations in the direct component of the plate current are manifested as a variation in the voltage drop across a resistance H9 in series with the plate circuit of tube H6. This drop is used to vary the grid bias of tube III in such a way that an increased said compressed range signals, varying the frequency of the generated wav in accordance with the intensity of the original signals, transmitting the resultant energy, receiving the transmitted energy and expanding the intensity range thereof in accordance with the frequency variations to compensate for the intensity range compression and produce a signal substantially proportional in intensity to the original signal.

2. In a signalling system of the kind described a transmitter comprising a microphone circuit, means for compressing the intensity range of signals impressed upon said microphone circuit, means for generating a high frequency carrier wave, means for modulating said wave with the compressed intensity range signals and means for varying the frequency of said carrier wave in accordance with the intensity of signals impressed upon said microphone circuit.

3. In a signalling system a circuit including a source of varying intensity signal energy, an intensity range compressor for compressing the intensity range of the signal energy connected to said circuit, a carrier frequency generator, a modulator associated with both said generator and said range compressor, a controlling circuit coupled to said first mentioned circuit including means for varying the frequency of the carrier wave generated by said generator in accordance with the intensity of the signal energy in said first mentioned circuit.

4. In a signalling system a microphone circuit an intensity range compressor circuit coupled to said microphone circuit and adapted to compress the intensity range of signals impressed on said microphone circuit, a source of high frequency carrier waves, a modulator adapted to modulate the carrier waves generated in said source with the compressed intensity range signals, a space discharge device having an input circuit coupled to said microphone circuit and an output circuit associated with said source of high frequency carrier waves said output circuit including means for varying the frequency of the high frequency carrier waves in accordance with the amount of compression, in said range compressor, of the intensity range of signals impressed on said microphone circuit.

5. In a signalling system a receiving circuit having means for variably amplifying incoming signal energy in accordance with variations of the incoming carrier frequency from a standard value, comprising a'local oscillator for generating energy of a frequency differing from said standard value by a fixed amount, means for combining the incoming energy with the locally generated energy for producing a beat note, a circuit tuned to the frequency of a beat note produced by combining energy of a frequency equal to said standard value with the locally generated frequency, means for impressing the beat note produced by combining said locally generated frequency with the incoming energy on said'tuned circuit, a controlling circuit associated with said first named means and said tuned circuit, said controlling circuit having means for controlling said first named means in accordance with the intensity of the beat note impressed upon said tuned circuit.

6. In a signalling system, a receiving circuit having means for variably amplifying incoming signal energy iii-accordance with variations from a standard value of the incoming carrier frequency, comprising a local oscillator adapted to generate energy of a frequency differing from said standard value by a fixed amount, means for combining the incoming energy with the cally generated energy for producing a beat note, means for producing a direct current varying in intensity proportional to the difference of intensity of the beat note' produced by the incoming frequency and the locally generated frequency and the beat note which would be produced by combining the locally generated frequency with the said standard frequency, a controlling circuit including a resistance, means for passing said produced direct current through said resistance and means controlled by the intensity of the current passing through said resistance for controlling the amplification of the incoming signal energy.

7. The method of cormnunicating signals of variable intensity which comprises, compressing the intensity range of the original signals, generating and modulating a carrier wave with the said compressed range signals, frequency modulating the generated wave in accordance with the intensity of the original signals, transmitting the resultant energy, receiving the transmitted energy and deriving therefrom the compressed range signals and expanding the intensity range oi the derived compressed range signals in accordance with the frequency modulations of the generated carrier wave to compensate for the intensity range compression and produce a signal substantially proportional in intensity to the oril signal.

8. In a system for communicating signals of variable intensity, means for compressing the intensity range of the original signals, means for generating a carrier wave, means for amplitude modulating said carrier wave, means for frequency modulating said carrier wave, one of said means being controlled by the intensity of said compressed intensity range signals and the other means being controlled by the degree of compression of the original signals.

9. In a signalling system, a receiving circuit including means for intercepting, frequency and amplitude modulated carrier energy, a translating circuit, means interposed between said intercepting means and said translating circuit comprising a circuit for deriving from the modulated carrier energy one of said modulations, and a circuit for deriving the other of said modulations, means for variably amplifying one of said derived modulations and means for controlling the degree of amplification thereof in accordance with said other modulations.

10. The steps in amethod of communicating signals of variable intensity which comprise, compressing the intensity range of the original signals, generating a carrier wave, varying the frequency of the generated carrier wave in accordance with the variations in intensity of the original signals, modulating said frequency modulated carrier wave by the compressed range signals, transmitting the resultant energy, receiving the transmitted energy and expanding the intensity range thereof in accordance with the frequency variations of the carrier wave to compensate for the intensity range compression of the signals at the transmitter and thereby produce signals substantially proportional in intensity to the original signals.

11. In a signalling system for communicating signals of variable intensity, means for producing signal equivalent electric energy flow the intensity of which is proportional to a predetermined varying characteristic of the signals desired to be communicated, means for generating a carrier wave, means for frequency modulating the carrier wave in accordance with variations oi. said electric energy fiow, means for compressing the range of the varying characteristic of the signals, means for an'iplitude modulating the carrier wave by the compressed range signals and means for transmitting the resultant energy.

12. In a signalling system for communicating signals of variable intensity from a transmitting point to a receiving point, means for producing signal equivalent electrical energy flow the intensity of which is proportional to a predetermined varying characteristic of the signals desired to be communicated, means for compressing the range of the varying characteristic of the signals, means for generating a carrier wave, means for frequency modulating the carrier wave and means for amplitude modulating the carrier wave, one of said last two named means modulating the carrier wave in accordance with variations of said characteristic of the original signals, the other of said last two means modulating the carrier wave in accordance with the compressed range signals, means for transmitting the resultant energy, means for receiving the transmitted energy and means for expanding the range of said characteristic thereof in accordance with one of said modulations to compensate for the range compression of the signals at the transmitter thereby producing signals substantially proportional to the original signals as regards said characteristics.

13. The steps in a method of communicating signals of variable intensity which comprise, producing signal equivalent electrical energy flow, the intensity of which is proportional to a predetermined varying characteristic of the signals to be communicated, compressing the range of the varying characteristic of the signals, generating a carrier wave, modulating the carrier wave by the compressed range signals, additionally modulating the carrier wave in accordance with variations of said characteristic of the original signals, and transmitting the resultant energy.

14. The steps in a method of communicating signals of varying intensity which comprise, producing signal equivalent electrical energy flow the intensity of which is proportional to a predetermined varying characteristic of the signals to be communicated, compressing the range of the varying characteristic of the signals, generating a carrier wave, modulating the carrier wave by the compressed range signals, additionally modulating the carrier wave in accordance with variations of said characteristic of the original signals, transmitting the resultant energy, receiving the transmitted energy and expanding the range of said characteristic thereof to compensate for the range compression of the signals at the transmitter thereby producing signals at the receiver substantially proportional to the original signals as regards said characteristic.

15.'In a communication system wherein a carrier wave is modulated by compressed range signailing currents and additionally modulated in accordance with the intensity of the original signals, means for receiving said modulated carrier wave, means for deriving therefrom said two modulations, means for amplifying one thereof and means for variably controlling the amplification factor of said amplifier means in accordance with the other modulation.

16. The steps in a method of communicating signals of variable intensity which comprise producing a flow of electrical energy the intensity of which is proportional to a predetermined varying characteristic of the signals to be communicated, acting upon said electrical energy so as to compress the range of the current flow variations caused by the varying characteristic of the signals, modulating a carrier medium by the compressed range energy, additionally modulating the carrier medium in accordance with the average variations in the intensity of said varying characteristic in the original signals, deriving the modulation energy from the carrier medium, separating the compressed range signal energy and the additional modulation energy, expanding the range of said characteristic of the separated compressed range signal energy in accordance with the derived additional modulation energy to compensate for said range compression to tnereby produce signals at the point of derivation substantially proportional to the original signals as regards said varying characteristic.

17 The steps in a method of impressing signals on a carrier medium which comprise producing a flow of electrical energy the intensity of which varies in accordance with intensity variations of the signals to be impressed, compressing the intensity range of the electrical energy thus produced, modulating a carrier medium by the compressed range electrical energy and additionally modulating the carrier medium in accordance with the average variations in the intensity of the original signals.

18. The steps in a method of deriving signals from a carrier medium which signals were impressed thereon in accordance with the method described in the next preceding claim which comprise deriving from the carrier medium the compressed range modulation and the additional modulation, variably amplifying the derived compressed range modulation and controlling the degree of amplification thereof in accordance with the additional modulation.

19. The steps in a method of communicating signal energy of variable intensity which comprise, amplifying the signal energy to a greater extent during intervals of low average intensity than during intervals of high average intensity, modulating a carrier medium with the variably amplified signal energy and additionally modulating the carrier medium in accordance with the average variations in the intensity of the signal energy.

20. The steps in a method of deriving signal energy from a carrier medium treated in accordance with the method described in the next preceding claim which comprise, deriving from the carrier medium the variably amplified signal energy modulation and the additional modulation, variably amplifyin the derived variably amplified signal energy and controlling the degree 01' amplification thereof in accordance with the derived additional modulation to thereby produce signal energy' substantially proportional to the original signal energy.

21. In a signalling system for communicating signal energy of variable intensity, means for variably amplifying the signal energy in such a way that amplification thereof is greater during intervals of low average intensity of the original signal energy than during intervals of high average intensity thereof, means for producing a carrier medium, means for modulating the carrier medium with the variably amplified signal energy, and means for additionally and relatively slowly modulating the carrier medium in accordaooaoso ance with the average variations in the intensity of the original signal energy.

22. In a signalling system arranged so as to derive signal energy from a carrier medium modulating in accordance with the system described in the next preceding claim, means for deriving from the carrier medium the variably amplified signal energy modulation and the additional modulation, means for variably amplifying the derived signal energy, and means for controlling the degree of amplification thereof in accordance with the derived additional modulation to thereby produce signal energy substantially proportional to the original signal energy.

23, The steps in a method of deriving signal energy from an intercepted carrier medium modulated in accordance with the method described in claim 19 which comprise, deriving from the intercepted {carrier medium the variably amplified signal energy modulation and the additional modulation, variably amplifying the derived signal energy and controlling the degree of amplification thereof in accordance with the combined effects of the derived additional modulation and the strength of the incoming carrier medium to thereby correct-for fading and at the same time produce signal energy substantially proportional to the original signal energy.

24. In a signalling system for communicating signal energy of variable intensity, means for variably amplifying the signal energy in such a way that amplification thereof is greater during intervals of low average intensity of the or iginal signal energy than during intervals of high average intensity thereof, means for producing additional energy, means for varying a characteristic of the additional energy proportional to variations in the average amplification of the signal energy, means for producing a carrier frequency, means for modulating the carrier frequency with the variably amplified signal energy and also with the additional energy, means for transmitting the resultant modulated carrier energy, means for intercepting the transmitted energy and deriving therefrom energy and the additional energy, means for variably amplifying the signal energy and controlling the degree of amplification thereof in accordance with the combined effects of the additional energy and the strength of the incoming carrier energy to thereby correct for fading and at the same time produce signal energy substantially proportional to the original signal energy.

SAMUEL G. FRANTZ. BRUNSON S. MCCUTCHEN.

both the signal 

